Genes against Drought - Max-Planck-Gesellschaft
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Genes
against Drought
In many regions of the Earth, agriculture is threatened by a lack of water. Therefore, new
plant varieties must be developed that are especially resistant to drought. For scientists
at the Max Planck Institute for Plant Breeding Research in Cologne, barley is an ideal
model for understanding the genetic strategies plants use to adapt to drought.
TEXT MARIA VON KORFF, MAX PLANCK INSTITUTE FOR PLANT BREEDING RESEARCH
P
lants have developed various proteins. These enzymes ensure that light, oxygen radicals, such as superox-
strategies to survive and grow cell proteins and membranes retain ides and peroxides, start to form. These
in the presence of drought. their normal structure and continue directly attack enzymes and mem-
For example, they avoid dam- to function. In addition, cells accumu- branes in the cell and destroy them.
age from a lack of water by late active substances, such as pro-
growing more roots to increase their line, sorbitol and glycine betaine, in ALTERNATIVES TO GENETICALLY
water uptake, or by reducing leaf their storage organelle, the vacuole. MODIFIED PLANTS
transpiration. Plants also store and re- These storage compounds reduce the
mobilize reserve carbohydrates and cells’ water loss. At the Max Planck Institute for Breeding
adjust their life cycles to survive in If all of these strategies fail, the os- Research in Cologne, we are studying
dry environments. motic pressure in the cell falls and how barley has adapted to dry condi-
Furthermore, plants can become the concentration of intracellular com- tions. We make use of the natural genet-
less sensitive to drought. Tolerance to pounds rises. The resulting osmotic ic diversity of cultivars and their close
drought stress is controlled by many stress damages the cell membrane and relatives (wild forms) as an alternative to
Photo: iStockphoto
genes, all of which improve the yield large molecules in the plant cells. Fur- studying transgenic crops. As barley and
for a given quantity of water. For thermore, if the lack of water prevents other cereals are genetically very similar,
example, plants can protect their photosynthesis, and the chloroplasts new findings in barley can be translated
cells from a lack of water with special continue to be exposed to strong sun- to other crops, such as wheat.
76 MaxPlanckResearch 3 | 10
ENVIRONMENT & CLIMATE_Breeding Research
Along with einkorn wheat, emmer Today, most variants still grow where trap the moist air above the leaf surface
wheat, flax and lentils, barley is one barley first originated and was later cul- and thus reduce transpiration and water
of the oldest cultivated plants. It was tivated by humans – in the Middle East loss from the plant. Barley can also
first cultivated about 10,000 years ago, region known as the Fertile Crescent, adapt its life cycle to the surrounding
when humans began to grow and select and in North and East Africa. Barley temperature and to the available water.
plants for food production. The elite thus holds great genetic potential for In dry, southern regions, for example,
barley varieties cultivated today are adaptation, which can be exploited to barley flowers early in the spring, ensur-
derived from the two-row wild form breed resistant varieties. ing that it completes its life cycle before
Hordeum vulgare L. ssp. spontaneum. Barley varieties that grow in very dry the onset of the summer heat. In tem-
The genus Hordeum comprises a total locations have developed special protec- perate latitudes, in contrast, barley de-
of 30 different wild varieties. After corn, tive mechanisms. Wild barleys from the velops more slowly, exploiting the long-
rice and wheat, barley is the fourth Fertile Crescent store more anthocy- er growth period. In Germany, barley
most important cereal in the world and anins in their stems, leaves and spikes. grows annually as spring barley or, like
has the widest geographical distribu- These pigments give the plant a red winter barley in the Mediterranean area,
tion. It grows in the dry regions of the color and protect it from excessive sun- over the winter.
Middle East, in Tibet at altitudes of over light, like a sunscreen. A dense cover of Today, four major genes are known
4,000 meters, in the sub-tropics and hairs on the stems and leaves also re- in barley that induce flowering when
at the polar limit of grain cultivation. flects the sunlight. In addition, leaf hairs the day length and temperature are ap-
3 | 10 MaxPlanckResearch 77
There are several phases in the development of barley flowers. First, vegetative growth tissue (meristem,
A) forms the flower meristem, B. From this is formed the spike with the meristem primordia (C), which
then develops into fertile florets (D) as the stem elongates. The duration of each of these phases varies
independently of the others and depends on both the environment and the genetic makeup of the plant.
Each developmental phase affects yield in a different way: the number of spikes per plant is
determined at the early developmental stage before the spike is completely developed.
The number of grains per spike is determined primarily during stem elongation.
A B C D
0.2 mm
0.2 mm
0.2 mm
0.2 mm
Physiological maturity
Main shoot elongates
meristem: Structure
Developing flower
Flower meristem
of spikes visible
Germination
(shoots)
Sowing
Flower
Plants per m² Spikes per plant
Timing of the
regulation and Spikelets per spike Grain weight
development Grains per spike
of yield Grains per m²
components
Total grain yield
propriate. The photoperiod response We are looking for genes that influ- ferences in reproductive development
gene Ppd-H1 in winter barley triggers ence individual phases of flower devel- and thus yield structure. The underly-
flowering as soon as day length increas- opment. This would allow flowering to ing traits and gene forms that cause this
es in spring. At the same time, the ver- be fine-tuned in different environ- variation are passed on to the offspring.
nalization gene Vrn-H2 counteracts ments in order to increase yield. With the aid of molecular markers, we
Ppd-H1; it permits flowering only when Drought shortens the time to flower- identify those regions in the barley ge-
the plant has been exposed to low tem- ing in barley. Long photoperiods af- nome that control spike development.
peratures. After a sufficient cold stimu- fect primarily the later reproductive As the barley genome has not yet been
lus, the vernalization gene Vrn-H1 in- stages, stem elongation and spike de- decoded, we align the identified ge-
duces the development of the repro- velopment. The extensive collection nomic regions with the rice reference
ductive meristem. In contrast, the of wild barleys from the Fertile Cres- genome, which has already been se-
vernalization gene Vrn-H3, like Ppd- cent held at our institute is a valuable quenced. This allows us to identify
H1, is thought to accelerate the late source of new genetic variants, as flowering time genes in barley, as rice
reproductive stages in barley. systematic breeding of high-yielding and barley are characterized by a simi-
varieties since the beginning of the lar gene content and gene order on the
MUTATIONS DELAY DEVELOPMENT last century has increasingly narrowed chromosomes.
IN BARLEY genetic variation in our elite varieties.
In terms of evolutionary history, FROM THE LABORATORY
In contrast to winter barley, the Ppd-H1 though, this is a short period of time, TO FIELD RESEARCH
gene is mutated in spring barley and is and most of the natural ancestors of
Graphic: dassel & schumacher
therefore inactive. Moreover, the Vrn- our recent cultivars can still be crossed We also use findings from plant ge-
H2 gene is deleted. Flower development with them. nome research on Arabidopsis thaliana
is thus delayed in spring barley under We investigated around 900 varie- because the pathways that trigger
long photoperiods, and does not re- ties of wild barley and crossed those flower development have already been
quire vernalization, allowing the plant that vary in their reproductive develop- thoroughly investigated in this plant.
to make use of the long growth period ment with German barley cultivars. As many of the genes and functions
in temperate climates. This gives rise to barley lines with dif- involved are also functional in barley,
78 MaxPlanckResearch 3 | 10
Scientists test the positive characteristics of wild barley, such as stress resistance, in crosses between wild
and cultivated barley in the field. Plants with slow stem and spike growth form particularly fertile flowers and
grains and thus provide a better yield.
it is possible to draw conclusions strategies barley uses to adapt to culations by the Intergovernmental
about the genetic regulation of flower drought. We then carry out detailed ge- Panel on Climate Change suggest that
development in barley. netic studies at our institute to identify harvest yields in these areas could be
Studies on the regulation of flower- the genes and gene regions that in- halved by 2020.
ing time in barley are first carried out crease the crop yield of barley under Central and Northern Europe are
under controlled conditions in the dry conditions. This information is not among the areas that might potential-
greenhouse, where we test the effect of only important for farmers in the Mid- ly benefit from climate change, as
individual environmental parameters – dle East, it also serves the breeding of heavier winter precipitation and high-
day length, temperature and water – on cultivated plants in other parts of the er average temperatures could increase
the individual genes and traits. Howev- world where they must adapt to in- agricultural production. For this to
er, we have to study the effects of the creasingly dry summers. happen, however, today’s crop plants
different gene forms in wild and culti- We are already experiencing an must be adapted to the new climate
vated barley in the field before they can accumulation of extreme weather con- conditions. This task is becoming in-
Photo: MPI for Plant Breeding Research
be applied in plant breeding. For this, ditions in connection with climate creasingly difficult, as it is not the sea-
we work with the Center for Agricultur- change. Global climate models are fore- sonal mean value that decides the
al Research in the Dry Areas (ICARDA) casting that, by the end of the 21st cen- quantity and quality of harvests, but
in Syria; ICARDA has the global man- tury, the Earth will be 2 to 5 degrees primarily the climatic extremes. For
date to research barley and agricultural Celsius warmer, and that heat waves, example, continental and southern re-
production in semi-arid regions. drought periods, floods and heavy pre- gions of Europe are already suffering
At this international agricultural re- cipitation will increase. The developing from longer dry periods in the summer
search center, we are examining, under countries in sub-Saharan Africa and months. But also in Germany, grain
natural conditions in the field, the in Asia will be particularly affected. Cal- harvests, with the exception of winter
3 | 10 MaxPlanckResearch 79
ENVIRONMENT & CLIMATE_Breeding Research
1
1 Pigments in the stem block part of the
solar radiation and protect the plant from
damage caused by too much light.
2 Barley protects itself from drought:
A thick layer of hairs acts like a
sunscreen and reduces the transpiration
of the plant.
3 Barley self-fertilizes and flowers when
the spikes are still in the leaf sheath.
Only after successful fertilization do
e
the spikes grow out of the leaf sheath and
the flowers open and reveal the anthers.
s
2 3 a
barley, have been stagnating for the tion was less than 150 mm in many of search in Cologne and Syria is thus to de-
past ten years. Therefore, also scien- the farming areas in the Fertile Crescent. code the genetic basis for stable yields
tists in Europe are researching the de- Under these conditions, drought-re- under extreme growing conditions.
velopment of plant varieties that max- sistant barley varieties still produce ap- Against this backdrop, in the future,
imize yield per unit of water used. proximately 500 kilograms per hectare. stable or even rising agricultural yields
In many areas of the Earth, water is To a German farmer with a yield of 60 to will depend on the successful develop-
in short supply. Water availability is 100 tons per hectare, this would mean ment of new cultivars. The cereals that K
thus the most important factor in agri- an almost total crop failure, but to a self- will become increasingly important are A
cultural production throughout the sufficient farmer in many regions of the those that are already an integral part
world. Increasing food production in Middle East, it means subsistence. They of extensive farming systems and that, g
e
the future depends primarily on wheth- are then not forced to sell their livestock due to their low water use, grow in dry
er agricultural areas can be supplied and look for work in the city. The most conditions – and these are mainly win- h
with sufficient water. In 2008, precipita- important objective of the breeding re- ter and spring barley. w
a
L
Photos: MPI for Plant Breeding Research (3)
GLOSSARY
Spring/winter barley Vernalization gene Fertile Crescent
Winter barley requires a cold period to develop in- (Latin vernus – spring) One of the regions in which humans originally settled
florescences. It is sown in late September in Central A gene that inhibits flower develop- and transitioned from the nomadic lifestyle to farming
Europe and harvested in July. Winter barley has a ment prior to sufficient exposure and livestock breeding. It covers parts of Lebanon,
20 percent higher yield, as it optimizes the use of of the plant to temperatures below Syria, Iraq, Iran and southeastern Turkey. Some of the
moisture in winter. Its share of barley production 10 degrees Celsius. In some plant globally most significant cultivated plants, such as
has thus been on the rise for years. Spring barley, varieties, there can be months wheat, barley, lentils and peas, and four of the five most
in contrast, is sown in March or April and harvested between the cold period and flower important domestic animals were domesticated here.
in August.Winter barley is used mainly for animal development. Most cereals need a The closely related wild forms of crop species are still
fodder; spring barley is used for malt. cold period before they flower. widespread in the Fertile Crescent.
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